Ext Tubes and Birds (1 Viewer)

Greetings one and all. :t:
I was wondering what's general good technique when using ext. tubes (I've got a Kenko set) to photograph birds.

It's an interesting alternative to a TC I've found, under the right circumstances of course. The limited knowledge I've acquired is that the 20mm tube works well for birds at around 15ft? (not very good at distance judging) on my 100-400mm as it gives you a little bit more magnification and unlike a TC on a 40D an ext tube will retain full AF. Could someone tell me what the equivalent focal length might be at 400mm with a 20mm tube, I'd like to know.

Anyway, you lose the ability to focus towards the inifinity end (not a problem if you're working at a fixed distance like at a feeding station), a small amount of light loss (less than a 1.4xTC? I think it is), doesn't work at the other zoom lengths only at 400mm (a prime would be best) but as there's no glass involved I don't believe there's any IQ loss. The 12mm would give you a little bit less mag but with more range and I've written off the 35mm as you'd have to be ludicrously close (captive birds are okay though). Stacking does work but with my stuff the IS goes funny and there's some hunting, If you can get close enough to a bird all 3 tubes will give you an awesome close-up but you'll be on a tripod and MF only. Not tried them for macro yet, waitng for the full on summer sun and associated insects.

Is my undertsanding about right? Anyone had similar experiences with them? I'd particularly like to hear from Mr Blake as he seems to use them a lot and his expertise is greater than mine (understatement of the year! :-O ).

Cheers all. B
Jaff

Although tubes do give some magnification with long lenses my understanding is that most who use them do so to reduce the min focus distance. I use them for macro stuff but did try them once on my 400mm f5.6 lens, from what I remember the increased magnification (focal length ?) is very minimal, certainly nothing like a 1.4 tc.

Jaff,

I use extension tubes all the time on astro scopes for the purpose of improving close focus not for magnification.

On my equipment here is how it works:

Magnification is a function of focal length. With my camera I get about 3x magnification for every 100mm of focal length on a lens. So on a 500mm lens I get about 15x magnification. If I add a 100mm extension tube I get 18x (3x6).

However it only takes a very small amount of extension to drastically change the focus point on a lens. So if I add only 20mm of extension I can change the close focus from 40 feet to 20 feet and lose focus at infinity. However because I only went from a 500mm lens to a 520mm lens the increase in magnification goes only from 15x to 15.6x.

So the long and the short of it is that a small amount of extension gives you a small increase in magnification while at the same time changing the close focus by a large amount - so much so that on my gear adding just 50mm of extension changes my 500mm scope into a macro lens. Not very practical for wildlife photography.

There is some interesting information at http://www.shutterfreaks.com/Tips/ExtensionTube.htm

I had realised in the past that reducing the focus on big primes was the primary use of ext tubes but for some reason when it came to writing the post I completely forgot, what a absolute doofus I am!
Anyway, I know that it would never be as much as a 1.4x TC but I didn't realise it was as little as what you said maxxxx. Never got round to taking a shot of something with and without them to see the effect but You're right I think I'll ditch them for using on birds.

They are however lookng very good on my new 50mm f1.8, when I put all 3 on, OMG! DOF was about 1mm or less but small things suddenly looked very big (especially with the live view!) so should make for some interesting messing about. Need to find a sleepy dragonfly so I can stick the lens right in his face! :-O

Thanks for the help all and for the link Arthur. Peace out. :hippy:
Adam

Jaff said:

You're right I think I'll ditch them for using on birds.

Click to expand...

They can be very effective if used properly for close-up work.

Following taken with a 560mm FL astro scope with extension tube to move the focus closer...

I wouldn't say extension tubes are an alternative to teleconverters, since the two are used for different purposes. Here are a few examples of closeup shots I took with extension tubes on long telephotos (either 400mm or 500mm). I have the Canon EF12 and EF 25 tubes.

http://www.pbase.com/gymell/image/84715943 (400mm)
http://www.pbase.com/gymell/image/84769506 (400mm)
http://www.pbase.com/gymell/image/84470927 (500mm +1.4x TC)

The DOF is very shallow, even on a tiny hummingbird.

I just had a thought.

Could you use an ext tube to effectively give you a shallower DOF which I always thinks make for a more interesting image, like your first one Liz. If a 20mm tube on my 100-400mm could make it more like an f4 instead of a f5.6 on the DOF then that would have some appeal to me, just gives you that bit more freedom to explore your creativity.

Maxxxx my SLR lens focusses down to 1.8m, at 100mm that is, 400mm will be a little more but still plenty so I don't need an ext tube to reduce the focus on my lens which is probably quite different than your astro scope.

Jaff said:

I just had a thought.

Could you use an ext tube to effectively give you a shallower DOF which I always thinks make for a more interesting image, like your first one Liz. If a 20mm tube on my 100-400mm could make it more like an f4 instead of a f5.6 on the DOF then that would have some appeal to me, just gives you that bit more freedom to explore your creativity.

Maxxxx my SLR lens focusses down to 1.8m, at 100mm that is, 400mm will be a little more but still plenty so I don't need an ext tube to reduce the focus on my lens which is probably quite different than your astro scope.

Click to expand...

Yes you'll get a shallower depth of field when using an extension tube.

Using an extension tube with the 100-400mm still reduces the minimum focus which enables a larger reproduction of the subject on the sensor for any given focal distance.

Mostly it's the 30mm tube that I use with the 100-400mm.

Yes, extension tubes reduce the DOF. The longer your focal length, the closer your subject, and the wider your aperture, the less DOF there is. When you add an extension tube, you can get closer to your subject and this reduces the DOF even further. The effect is more apparent with a long focal length.